LINQ - ASP.NET 核心中 int 列上的通配符

Question

I have a table that returns records from the database. The users have various dropdowns and input boxes where they can search specific results within columns. I have an input box that searches a column that takes an int and null values. If the user does not specify anything inside of the input box, I want to return all applicable records from that column.

Either the value of the classroom size input box is an integer, or it is set as a wildcard if the user does not specify. This is why I run into a cast issue.

The way I have it set it up now returns a 400 status if I do not specify an integer in the input box. Please let me know how I can accomplish my goal, thank you for your time!

View:

@model IEnumerable<MyApp.Models.tblClassrooms>

    <div>
    <form method="get" role="form" asp-controller="Classroom" asp-action="Index">
        <label>Class Size</label>
        <input type="search" value="@ViewData["sizeSearch"]" name="sizeSearch" />
        <input asp-controller="Classroom" asp-action="Search" value="Search" type="submit" />
    </form>
    </div>

Controller:

[HttpGet("[action]")]
public async Task<IActionResult> Search(string sizeSearch)
{
    ViewData["sizeSearch"] = sizeSearch;

    var query = from x in _db.tblClassrooms
                .Where(x => x.ID == 10)
                select x;

    if (string.IsNullOrEmpty(sizeSearch))
    {
        //set a variable equal to a 'wildcard'
        //this is where I run into a cast issue
    }

    //adding to the query above, search by that table, where the ID is 10,
    //furthermore, search by either the classroom size or the wildcard
    query = query.Where(x =>
    x.ClassSize.Equals(sizeSearch));

    return View("Index", await query.AsNoTracking().ToListAsync());

}

Note: I am using ID = 10 for testing purposes. Please keep in mind that I have other values that I am also searching by.

Answer 1

If I understand your usage of the word 'wildcard' correctly, you could just omit the second where clause:

if (!string.IsNullOrEmpty(sizeSearch))
{
    query = query.Where(x => x.ClassSize.Equals(sizeSearch));
}

This way, if nothing is passed into sizeSearch , you will not be filtering your query by it.